Chapter 8.3 The Process of Photosynthesis

Question 1

What happens during the Light-Dependent Reactions?

Answer 1

The L-D Rxn’s use energy from sunlight in order to produce oxygen and convert energy carriers NADP⁺ and ADP into the high energy carriers NADPH and ATP .

Summary:=

1) Split Water (produce O₂ and H⁺ in thylakoid space)
2) Photosystem II absorbs Photon to energy electrons
3) Electron Transport Chain uses some energy to actively pump H⁺ ions into the thylakoid space from the stroma
4) Electrons are re-energized by Photosystem I and go to form NADPH in the stroma.
5) H⁺ ions in thylakoid space push through ATP Synthase due to concentration gradient (facilitated diffusion powered) which produces ATP in the stroma.

Question 2

What is a photosystem?

Answer 2

A cluster of chlorophyll and proteins found in the thylakoid membrane which help to take the electrons from the splitting of water and absorb energy from photons of sunlight to energize those electrons.

Question 3

What is the Electron Transport Chain? (ETC)

Answer 3

The ETC is the series of electron carrier proteins that shuttle high-energy electrons during ATP-generating reactions along the Thylakoid Membrane.

Question 4

What is ATP Synthase?

Answer 4

ATP = Adenosine Triphosphate

Synthase = Enzyme which makes

ATP Synthase is a cluster of proteins which span the Thylakoid Membrane and allow H⁺ ions to pass through it (due to the concentration gradient already established) which produces ATP.

Question 5

What happens during the Light-Independent Reactions?

Answer 5

During the L-I Rxns, NADPH and ATP from the L-D Rxns are used to produce high energy sugar (glucose) from Carbon Dioxide in a process known as the Calvin Cycle.

Summary:

1) 6 Carbon Dioxide molecules are combined with 6 5-carbon molecules which split apart into 12 3-carbon high energy molecules.
2) During the cycle ATP and NADPH are used to combine 2 of these 12 3-carbon high energy molecules into glucose (C₆H₁₂O₆)
3) The used up energy carriers NADP⁺ and ADP go back to the L-D Rxns to keep the cycle going and the now 10 3-carbon energy molecules recombine to form the original 6 5-carbon molecules to regenerate the starting molecules necessary for the Calvin Cycle to begin again.

Question 6

What factors affect photosynthesis?

Answer 6

Temperature, light intensity, and the availability of water will alter the rate of photosynthesis.

Question 7

What is different about C4 photosynthesis?

Answer 7

This type of photosynthesis is adapted in plants to be able to caputre Carbon Dioxide which is in low concentrations in the atmosphere. (examples include corn, sugar cane, and sorghum)

Can work under intense light, extreme temperatures, but requires more ATP to be used.

Question 8

What is different about CAM Plants?

Answer 8

CAM Plants are members of the Crassulacae family which have adapted to do photosynthesis in very dry climates (where losing water would be deadly) who only open their tiny pores in the leaves (called stomata) during the night time for gas exchange when temperatures are low. They capture the CO₂ necessary for photosynthesis by producing an organic compound named Crassulacae Acid. Theprocess of using captured CO₂ during the daytime while the leaves are sealed shut is called Crassulacae Acid Metabolism. Examples include pineapple plants and desert cacti.

Question 9

What is the Calvin Cycle?

Answer 9

The Calvin Cycle is the reactions which do not depend on the sun (L-I Rxns) which fixate the carbon from CO₂ into the high energy sugar glucose (C₆H₁₂O₆) from the high energy carriers NADPH and ATP.